Abstract
ABSTRACTThe interaction of trypsin with acteoside was studied using ultraviolet visible absorption, fluorescence, synchronous fluorescence, circular dichroism techniques, along with molecular docking method. The fluorescence experiments indicated that acteoside quenched the intrinsic fluorescence of trypsin via a combined quenching process (static and dynamic quenching). The binding constant of acteoside to trypsin obtained was 2.50 × 105 L mol−1 at 298 K and the number of binding site was about one under the same experimental condition. The thermodynamic functions ΔH° and ΔS° of the binding process were 8.79 kJ mol−1 and 132.58 J mol−1 K−1, respectively, which indicated that the hydrophobic force was the main acting force between them. Ultraviolet–visible, synchronous fluorescence together with circular dichroism spectra studies demonstrated that the interaction of acteoside with trypsin lead to a loosening and unfolding of the protein backbone with partial β-sheet structures being transformed into α-helix structures. All these experimental results were validated and explained reasonably by docking studies. And the molecular docking results further illustrated that besides hydrophobic forces, hydrogen bonds also played an important role in the stabilization of the acteoside–trypsin complex. Results from this study should be helpful to make full use of acteoside in the food industry and be useful to the design of the drugs for the diseases related to trypsin.
Highlights
Herbs have attracted a great deal of interests as a source for the development of drugs and one of the key ingredients in functional foods
The intensity of the peak at 278 nm increased with slight blue shifts as the increase of the concentration of acteoside, indicating that acteoside can bind to trypsin and a acteoside–trypsin complex is formed, which results in the increase of the probability of π–π* transition of aromatic amino acid residues in trypsin, and the intensity of absorbance peak around nm.[25]
These results elucidate that the interaction between acteoside and trypsin results in a conformational change of trypsin with partial β-sheet structures being transformed into α-helix structures, which is concordant with the experimental results obtained from previous UV spectral studies
Summary
Herbs have attracted a great deal of interests as a source for the development of drugs and one of the key ingredients in functional foods. Herbal medicines derived from plant extracts are increasingly being utilized to treat a wide variety of clinical diseases.[1] Acteoside (see Fig. 1) contains the hydroxyphenylethyl and caffeoyl moieties which are well-known antioxidants and was reported to possess various biological activities, such as anti-stress and immunosuppressive properties, anti-nephritis, cardioactive, and antitumor activities.[2]. Proteases are a kind of important proteins which can cleave the covalent peptide bond between amino acids.[3] The water-soluble globular protein, trypsin (EC 3.4.21.4), belongs to serine protease family and exists in form of trypsinogen in the pancreas of all vertebrates.
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